SainSmart GRBL - Setting Vref; Setting Motor Current Reference

12
3 – Setting V
ref
Setting V
ref
Before connecting stepper motors to the control module, the maximum motor currents for the stepper motors used must
first be set on the control module using the appropriate miniature potentiometers. For the stepper motor drivers of the
type A4988 used in the control module, the formula for determining the maximum motor current is:
I
max
(maximum motor current) = V
ref
/ (8 x R
sense
)
R
sense
has a resistance value of 0,1Ω for this control module.
Converted to V
ref
is makes the following formula:
V
ref
= I
max
(maximum motor current) x 0,8Ω
Thus, for an ordinary stepper motor with a maximum motor current of 0.8A this results to a V
ref
value of 0.8A x 0.8Ω =
640mV.
To set the reference voltage V
ref
, you need a multimeter and an adjustment screwdriver. Connect the COM port of your
multimeter to GND. GND is, for example, on all pins of the 16-pin male connector pointing to the lower edge of the
board. Hold the V connector tip of your multimeter to the middle connector of the corresponding miniature potentiometer
(X, Y or Z). Then set the required voltage value V
ref
on the miniature potentiometer with the adjustment screwdriver.